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Use

The cardinality (n:m) describes the foreign key relationship with regard to the number of possible dependent records (records of the foreign key table) or referenced records (records of the check table).

The left side (n) of the cardinality is defined as follows:

  • n=1

    There is exactly one record assigned to the check table for each record of the foreign key table.

  • n=C

    The foreign key table can contain records that do not correspond to any record of the check table because the foreign key field is empty. This can occur, for example, if the field of the foreign key table is optional, in which case it does not have to be filled.

The right side (m) of the cardinality is defined as follows:

  • m=1

    There is exactly one dependent record (record of the foreign key table) for each record of the check table.

  • m=C

    There is at most one dependent record for each record of the check table.

  • m=N

    There is at least one dependent record for each record of the check table.

  • m=CN

    There can be any number of dependent records for each record of the check table.